Guava’s Strings Class

In the post Checking for Null or Empty or White Space Only String in Java, I demonstrated common approaches in the Java ecosystem (standard Java, Guava, Apache Commons Lang, and Groovy) for checking whether a String is null, empty, or white space only similar to what C# supports with the String.IsNullOrWhiteSpace method. One of the approaches I showed was a Guava-based approach that made use of the Guava class Strings and its static isNullOrEmpty(String) method. In this post, I look at other useful functionality for working with Strings that is provided by Guava’s six ‘static utility methods pertaining to String’ that are bundled into the Strings class.

Using Guava’s Strings class is straightforward because of its well-named methods. The following list enumerates the methods (all static) on the Strings class with a brief description of what each does next to the method name (these descriptions are borrowed or adapted from the Javadoc documentation).

• Strings.isNullOrEmpty(String)
  • ‘Returns true if the given string is null or is the empty string.’
• emptyToNull(String)
  • ‘Returns the given string if it is nonempty; null otherwise.’
• nullToEmpty(String)
  • ‘Returns the given string if it is non-null; the empty string otherwise.’
• padStart(String,int,char)
  • Prepend to provided String, if necessary, enough provided char characters to make string the specified length.
• padEnd(String,int,char)
  • Append to provided String, if necessary, enough provided char characters to make string the specified length.
• repeat(String,int)
  • ‘Returns a string consisting of a specific number of concatenated copies of an input string.’

 
isNullOrEmpty

Guava’s Strings.isEmptyOrNull(String) method makes it easy to build simple and highly readable conditional statements that check a String for null or emptiness before acting upon said String. As previously mentioned, I have briefly covered this method before. Another code demonstration of this method is shown next.

Code Sample Using Strings.isNullOrEmpty(String)

The output from running the above code is contained in the next screen snapshot. It shows that true is returned when either null or empty String (”) is passed to Strings.isNullOrEmpty(String).

nullToEmpty and emptyToNull

There are multiple times when one may want to treat a null String as an empty String or wants present a null when an empty String exists. In cases such as these when transformations between null and empty String are desired, The following code snippets demonstrate use of Strings.nullToEmpty(String) and Strings.emptyToNull(String).

nullToEmpty and emptyToNull

The output from running the above code (shown in the next screen snapshot) proves that these methods work as we’d expect: converting null to empty String or converting empty String to null.

padStart and padEnd

Another common practice when dealing with Strings in Java (or any other language) is to pad a String to a certain length with a specified character. Guava supports this easily with its Strings.padStart(String,int,char) and Strings.padEnd(String,int,char) methods, which are demonstrated in the following code listing.

padStart and padEnd

When executed, the above code pads the provided Strings with underscore characters either before or after the provided String depending on which method was called. In both cases, the length of the String was specified as ten. This output is shown in the next screen snapshot.

repeat

A final manipulation technique that Guava’s Strings class supports is the ability to easily repeat a given String a specified number of times. This is demonstrated in the next code listing and the corresponding screen snapshot with that code’s output. In this example, the provided String is repeated three times.

repeat

Wrapping Up

The above examples are simple because Guava’s Strings class is simple to use. The complete class containing the demonstration code shown earlier is now listed.

GuavaStrings.java

The methods for padding and for repeating Strings do not take kindly to null Strings being passed to them. Indeed, passing a null to these three methods leads to NullPointerExceptions being thrown. Interestingly, these are more examples of Guava using the Preconditions class in its own code.

Conclusion

Many Java libraries and frameworks provide String manipulation functionality is classes with names like StringUtil. Guava’s Strings class is one such example and the methods it supplies can make Java manipulation of Strings easier and more concise. Indeed, as I use Guava’s Strings‘s methods, I feel almost like I’m using some of Groovy’s GDK String goodness.
 

Reference: Guava’s Strings Class from our JCG partner Dustin Marx at the Inspired by Actual Events blog.

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